6 INTELLECT CHAP. 
ing therefore a less specialised condition of the limbs. It is 
an interesting fact that the angulation of the limbs is to some 
extent obliterated in very bulky creatures, and almost entirely 
so in the elephants (see p. 217), which seem to need strong and 
straight pillars for the due support of their huge bodies. 
The alertness and general intellectual superiority of mammals 
to all animals lying below them in the series (with the exception 
of the birds, which are in their way almost on a level with the 
Mammalia) are seen by their active and continuous movements. 
The lengthy periods of absolute motionlessness, so familiar to 
everybody in such a creature as the Crocodile, are unknown among 
the more typical Mammala except indeed during sleep. This 
mental condition is clearly shown by the proportionate develop- 
ment of the external parts of all the organs of the higher senses. 
The Mammalia as a rule have well-developed, often extremely 
large, flaps of skin surrounding the entrance to the organ of 
hearing, often called “ears,” but better termed “pinnae.” These 
are provided with special muscles, and can be often moved and 
in many directions. The nose is always, or nearly always, very 
conspicuous by its naked character; by the large surface, often 
moist, which surrounds the nostrils; and again by the muscles, 
which enable this tract of the integument to be moved at will. 
The eyes, perhaps, are less marked in their predominance over the 
eyes of lower Vertebrates than are the ears and nose; but they 
are provided as a rule with upper and lower eyelids, as well as 
by a nictitating membrane as in lower Vertebrates. The apparent 
predominance of the senses of smell and hearing over that of 
sight appears to be marked in the Mammalia, and may account 
for their diversity of voice as well as of odour, and for the 
general sameness of coloration which distinguishes this group 
from the brilliantly-coloured birds and reptiles. The head, too, 
which bears these organs of special sense, 1s more obviously 
marked out from the neck and body than is the case with the 
duller creatures occupying the lower branches of the Vertebrate 
stem. 
The Hair.—The Mammalia are absolutely distinguished from 
all other Vertebrates (or, for the matter of that, Invertebrates) 
by the possession of hair. To define a mammal as a Vertebrate 
with hair would be an entirely exclusive definition ; even in the 
smooth Whales a few hairs at least are present, which may be 
